1. Field of the Invention
The present invention relates to an ultrasound diagnostic system using a capacitive micromachined ultrasonic transducer.
2. Description of the Related Art
An ultrasonic transducer using a capacitive micromachined ultrasonic transducer (hereinafter referred to as “C-MUT”), which is different from a piezoelectric transducer, has recently been developed, and an ultrasound diagnostic system is being proposed which is used for an inspection using ultrasound with an ultrasound probe or ultrasound endoscope mounted with the ultrasonic transducer connected therewith.
The C-MUT has a structure in which one cavity is provided in a silicon substrate and electrodes are provided on and below the cavity, and by applying an ultrasound drive signal (or transmission signal) together with a bias voltage to these electrodes, a film above the cavity is made to vibrate to transmit ultrasound, a returned echo signal is detected with the upper film and transmission/reception of ultrasound is thereby realized.
Since the C-MUT has a structure using a capacitive micromachined ultrasonic transducer, the C-MUT is liable to store charge and when the C-MUT continuously drives ultrasound for a long time, a certain amount of charge is accumulated.
In order to alleviate disadvantages of the deterioration in electric acoustic conversion efficiency in the upper film due to the accumulation of charge, International Publication No. 2007/029357 as a first related art discloses that sensitivity during transmission/reception is corrected by monitoring the amount of charge.
Furthermore, as a second related art, International Publication No. 2005/120359 discloses means for adjusting a DC bias voltage when the DC bias voltage is superimposed on a high frequency pulse as a transmission signal and applied to the C-MUT.